1. Field of the Invention
The present invention relates to systems for administering solutions to patients in such a manner as to decrease the risk that air bubbles will be inadvertently provided to the patient. More specifically, the present invention relates to a system for optically detecting bubbles in solution being provided to a patient.
2. State of the Art
Parenteral and Enteral feeding systems are used to provide solutions to patients. In parenteral systems, solutions such as balanced saline solutions are administered to the patient""s circulatory system. Enteral feeding systems are provided for patients who, for one reason or another, are unable to eat for themselves.
One common concern with both parenteral and enteral feeding systems is that it is undesirable for large quantities of air to be provided with the solution. In enteral systems, excessive air may irritate the digestive system of the patient and complicate other medical conditions. Additionally, the air can render the volumetric calculations of the enteral feeding pump inaccurate.
In parenteral applications, the risk can be much greater. While air in a parentral infusion line is undesirable, large quantities of air can cause serious problems in the vascular system. In extreme cases, excessive air can even cause death of the patient. Thus, it is critical in parenteral application that air not be delivered to the patient""s vascular system.
In addition to the health concerns posed by the air being released into the patient""s body, the presence of air in the parenteral or enteral feeding tube also means that the desired solution is not being delivered to the patient. Each cubic centimeter of air is a cubic centimeter of enteral feeding solution, medication, etc. which is not delivered to the patient. Without being able to detect the quantity of air passing through the system, the system is unable to accurately determine the actual amount of solution which has been delivered to the patient. Over a prolonged period of time, even modest amounts of air passing through the system can cause significant disparities in the amount of solution the system indicates to be delivered and the actual amount delivered.
There are numerous mechanisms available for detecting air in liquid passing through a tube. Many of these mechanisms provide marginal accuracy or are complex to use. Others, while relatively accurate, require considerably more power draw than is necessary. Yet other air detectors do not provide an inherent integrity check to prevent failure of the sensor from giving erroneous information regarding air in the conduit.
While all of the above are disadvantageous, a principle disadvantage of most air detectors which are used in enteral feeding pumps and the like is the cost. Most enteral feeding pumps utilize ultrasonic sensors to check for bubbles. Such sensors, however, can cost fifty times or more the cost of an optical sensor.
Thus, there is a need for an improved sensor for determining the presence of bubbles, which is less expensive, and which is easy to operate.
It is an object of the present invention to provide an improved sensor for detecting bubbles in a conduit;
It is another object of the present invention to provide such a sensor which is easy to make and use.
It is yet another object of the present invention to provide such a sensor which utilizes refraction of light to determine the presence of air within the conduit.
It is still another object of the present invention to provide such an optical sensor which is relatively inexpensive.
The above and other objects of the invention are realized in specific illustrated embodiments of an optical air/liquid sensing system which utilizes a sample cell. The sample cell has a pair of sidewalls which refract light into the liquid in the conduit at such an angle that the light passes out of the sample cell in a first direction when no air is present in the conduit, and in a second direction when air is present in the conduit.
The sample cell is disposed between an optical emitter and an optical detector. Light is emitted from the optical emitter and is refracted as it passes through the sample cell. The presence of air within the sample cell changes the refraction of light, thereby changing the light received by the optical detector. It should be appreciated that, as used herein, the term light is not limited to electromagnetic radiation in the spectrum visible to humans. To the contrary, a preferred embodiment of the invention utilizes infrared radiation.
In accordance with one aspect of the present invention, the amount of air in the conduit affects the amount of light refracted in the second direction. The amount of light refracted into the first direction versus the amount refracted in the second direction indicates the relative amount of air in the conduit.
In accordance with another aspect of the invention, the sample cell is configured and disposed to always allow some light to pass through the sample cell and to be received by the optical detector. If no light is detected by the optical detector, the system is readily able to determine that the system has failed.
In accordance with another aspect of the invention, the sample cell is situated so that all of the light emitted from the optical emitter does not reach the optical detector. Thus, if the optical detector indicates that nearly all of the light emitted from the optical detector has been received, the optical sensor system can readily determine that the sample cell is not properly loaded between the optical emitter and optical detector of the sensor.
In accordance with another aspect of the invention, the exterior of the sample cell is triangular. The shape of the sample cell regulates the flow of light through the sample cell and thereby directs light to the optical detector depending on whether air is present in the conduit.
In accordance with still yet another aspect of the present invention, a housing is provided and spaced apart from the sample cell by an air channel. As with the shape of the sample cell, the housing helps to direct light through the sample cell at a desired angle to facilitate the determination of whether air is present in the conduit in the sample cell.
Preferably, the housing is formed of a similar material to the sample cell and is disposed at an angle parallel to the sidewalls of the sample cell. This provides for the refraction of light at desired angles through the sample cell.
In accordance with another aspect of the present invention, a sample cell container is provided with a channel disposed therein. Properly mounting a flexible tube in the channel causes the tube to form first and second sidewalls which are disposed at desired angles to refract light in one direction when a solution is present, and to refract light in a second direction, i.e. toward an optical signal detector, when the conduit is filled with air.
In a preferred embodiment of the invention, the sample cell has sidewalls which are disposed at an angle of between about 45 and 100 degrees relative to one another are disposed at the same acute angle relative to a plane extending from the optical signal emitter and the optical signal detector. More preferably, the two sidewalls are disposed at an angle of 60 degrees from one another and are disposed at the same relative acute angle from a horizontal or other plane passing through the sample cell from the optical signal emitter and the optical signal detector. By same angle it is meant that each sidewall has a similar acute angle from the plane, although they are in opposite directions.
In accordance with another aspect of the invention, it has been found that the sample cell can be used to determine the presence of air so long as the sample cell wall is less than normal from the plane along which the light is omitted. The closer the sample cell wall is to normal, however, the further away the optical sensor components must be from the sample cell wall. Additionally, the positions of the optical signal emitter and the optical signal detector can be adjusted to ensure light is refracted to the optical sensor when air is present, but not when liquid is present, or vice versa.